Optical microscopes are used in conjunction with electrical testers to diagnose process and design faults in integrated circuits. However, diffraction limits optical microscopy through the substrate of an integrated circuit to spatial resolutions that are insufficient to resolve the smallest features in the integrated circuit. Furthermore, contribution to the optical microscopy images by multiple transistor and interconnect layers in the integrated circuit prevents accurate longitudinal fault localization and accurate lateral registration to the circuit.
Thus, there is a need for improved lateral and longitudinal spatial resolution in optical diagnostics of process and design faults in integrated circuits in order to increase the information gathered by the optical diagnostics.